I. Field of the Invention
The present invention relates to a coil wire and, more particularly, to a coil wire used for an excitation winding of a sealed electric device such as an electromagnetic relay.
II. Description of the Prior Art
A conventional coil wire for an excitation winding of a sealed electric device such as an electromagnetic relay obtained by sealing the excitation winding together with contact members in a case in a given hermetic state so as to electromagnetically drive the contact members is prepared in the following manner. An electrically insulating coating material such as a polyurethane resin or polyimide resin which is dissolved in a solvent mixture comprising a solvent containing cresol, a phenol and a benzene nucleus is applied to the outer surface of a conductor, such as copper, and is baked. Thereafter, a lubricant such as paraffin or spindle oil is applied to the outer surface of the insulation film to smoothen the surface of the resultant wire and hence to prevent a disconnection during manufacture of the winding. However, when an enamel coil wire of the type described above is used for the excitation winding of a plastic sealed relay, the residual solvent in the insulation film of the winding and the lubricant component are evaporated upon operation of the relay to generate organic gases inside the sealed case. As a result, the contact resistance of the contact members which are closed/opened with respect to each other tends to increase, and contact activation will result. Therefore, contact wear is greatly increased.